1. Field of the Invention
The present invention relates to a process for producing a honjozo-type (which means that flavor is developed without use of any artificial additives) soy sauce having a rich flavor.
2. Background Art
A typical example of rich-flavor soy sauce is a saishikomi-shoyu (saishikoini is a Japanese word which means “double brewed”) or kanro-shoyu (kanro is a Japanese word which means nectar). The saishikomi-shoyu is produced through several steps, including adjustment of salt concentration of a raw regular soy sauce by use of salt water, incorporation of soy sauce koji (which means an enzyme preparation produced by growing a koji mold on a mixture of roasted-crushed wheat and boiled soybeans for soy sauce) into the raw regular soy sauce, and fermentation-aging of the resultant mixture for several months with or without addition of yeast. The thus-produced saisbikomi-shoyu is characterized in that it has a high nitrogen content (normally, TN (total nitrogen)≧2 wt. % (W/V)) and that it has a dark color and a rich taste.
However, because of a process-related factor unique to the production process of the saishikomi-shoyu, the produced saishikomi-shoyu tends to have a flavor different from that of a well-accepted, typical regular soy sauce. That is, in the manufacture of a saishikomi-shoyu, salt water (which is generally employed for producing a regular soy sauce) is replaced by regular soy sauce, and this replacement hinders the growth of yeast in moromi mash, to thereby slow the alcoholic fermentation process of moromi mash. The slowed process produces a product having a different flavor, which is less favored by consumers who are accustomed to the flavor of regular soy sauce.
Hitherto, a variety of attempts have been made to overcome the above-mentioned drawbacks involved in saishikomi-shoyu and to produce a rich-flavor soy sauce which does not have such a problem. Some such attempts are: (1) a process including separating a liquid from moromi mash in the early stage of preparation for the fermentation process; adding soy sauce koji to the separated liquid which serves as shikomi-mizu (i.e., water which is used to prepare moromi mash in a large container; hereinafter referred to simply as shikomi water); and then performing routine fermentation and aging processes (Japanese Patent Publication (kokoku) No. 20/1989); (2) a process including extracting, with water or hydrated alcohol, oligosaccharides and organic acids from defatted soybeans serving as a raw material; heating the residue for denaturing proteins; mixing with a carbohydrate source material; inoculating the resultant mixture with a koji mold to thereby prepare koji; adding salt water to the koji for preparing the moromi mash, and then performing routine fermentation and aging processes (Japanese Patent Application Laid-Open (kokai) No 123132/1993); (3) a process including steaming soybeans, followed by extraction with water or warm water, to thereby yield a sugar-containing solution; preparing salt water using, as part or the entirety of shikomi water, the sugar-containing solution; adding the thus-prepared salt water to soy sauce koji which has been obtained through a routine method for preparing moromi mash; and then performing routine fermentation and aging processes (Japanese Patent No. 3274544); (4) a process for producing a rich-flavor soy sauce by mixing soy sauce koji and soy sauce, fermenting the mixture, followed by aging, wherein the soy sauce koji is prepared from rice, and the soy sauce (serving as a raw material) is a rice-based shoyu, followed by routine fermentation and aging processes (Japanese Patent Application Laid-Open (kokai) No. 179083/1998); and (5) a process for producing a saishikomi-shoyu, in which the temperature of moromi mash is maintained at 15 to 23° C. from the beginning to the end of the fermentation and aging process, with the fermentation and aging process being effected by the addition of yeast capable of inducing specific alcoholic fermentation (Japanese Patent Application Laid-Open (kokai) No. 2001-61437).
However, all these conventional processes are not necessarily convenient, because they require any of the following steps: (1) a pressing step of pressing moromi mash in the early stage of fermentation; (2) an extraction step of extracting, with water or hydrated alcohol, oligosaccharides and organic acids from defatted soybeans serving as a raw material; (3) a steaming step of soybeans, after which water or warm water is used to yield a sugar-containing solution; (4) a provision step in which rice-based koji and rice-based shoyu are prepared in advance; and (5) an isolation step for obtaining yeast capable of inducing specific alcoholic fermentation.
In view of the foregoing, the present inventors have devoted their research efforts to provision of a convenient production process of a rich-flavor soy sauce, which uses the processing steps of conventional soy sauce brewing, without requiring any special treatment.
During the course of their research, they have found that addition of soy sauce and soy sauce koji at an appropriate point in time during fermentation of ordinary regular soy sauce and subsequent aging successfully provides an excellent soy sauce which has a light color and yet gives a rich flavor comparable to that of regular soy sauce, has a total nitrogen content of not less than 2% (W/V), and has a taste comparable to that of saishikomi-shoyu. The present invention has been achieved on the basis of this finding.